External Core Complex Interfaces
e200z3 Power Architecture Core Reference Manual, Rev. 2
Freescale Semiconductor
7-33
from the slave device for addr
y
is provided on the p_[d,i]_hrdata inputs. The slave device responds
by asserting p_[d,i]_hready to indicate the cycle is completing, and it drives an OKAY response.
Another read transfer request is made during C3 to addr
z
(p_[d,i]_htrans = NONSEQ), and
because the access to addr
y
is completing, it is considered taken at the end of C3.
•
Clock 4 (C4)—During C4, the addr
z
memory access takes place, using the address and attribute
values that were driven during C3 to enable reading of one or more bytes of memory. Read data
from the slave device for addr
z
is provided on the p_[d,i]_hrdata inputs. The slave device responds
by asserting p_[d,i]_hready to indicate the cycle is completing, and it drives an OKAY response.
Because the CPU has no additional outstanding requests, p_[d,i]_htrans indicates IDLE and the
address and attribute signals are undefined.
7.5.1.2
Read Transfer with Wait State
shows an example of wait state operation. Because signal p_[d,i]_hready for the first request
(addr
x
) is not asserted during C2, a wait state is inserted until p_[d,i]_hready is recognized (during C3).
Meanwhile, a subsequent request was generated by the CPU for addr
y
which is not taken in C2, because
the previous transaction is still outstanding. The address and transfer attributes remain driven in cycle C3
and are taken at the end of C3 because the previous access is completing. Data for addr
x
and a ready/OKAY
response are driven back by the slave device. In cycle C4, a request for addr
z
is made. The request for
access to addr
z
is taken at the end of C4, and during C5, the slave device provides the data and a
ready/OKAY response. In cycle C5, no further accesses are requested.
Figure 7-4. Read with Wait-State, Single-Cycle Reads, Full Pipelining
nonseq
nonseq
nonseq
idle
addr x
addr y
addr z
single
single
single
data x
data y
data z
okay
okay
okay
okay
okay
1
2
3
4
5
6
m_clk
p_htrans
p_addr,p_hprot
p_hsize
,
p_hbstrb
, etc
p_hburst
p_hunalign
p_hwrite
p_hrdata
p_hwdata
p_hready
p_hresp
Содержание e200z3
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